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  1. #1

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    Calling the Yamaha experts!

    Back in April I bought a 96 waveraider 760 that had a bad pto side piston. (Piston looked to have been lean seized). It was my first foray into the world of two stroke engine rebuilding. Rebuilt using a set of WSM 84.25mm pistons, cylinders bored and honed correctly, and honed to set piston clearance per Yamaha spec. Also picked up a good used crank on ebay for $125.00. After break in, compression is 176 mag side, 165 pto side. (Compression is supposed to be lower on the pto side on this particular engine). Also had head milled to correct flatness, and the pto side dome was cleaned of all detonation marks. Seems to run great on 87 octane gas. Also rebuilt carbs using genuine mikuni kits, replaced all fuel lines, updated the oil injection system with new line and pinch clamps.
    I bought it at a steal, and repaired it before actually learning anything about the two strokers. And, it does run great now. Now, here is my question........
    I rebuilt the engine using permatex #2 (turboseal) to seal the cases, not threebond, used the cheapo crank seals off ebay (I was on a budget back then), and no pressure test of the engine. What do you guys think? Is it a ticking time bomb? Its cheaper to go in and correct the oversights while the engine is running well as opposed to having to buy a crank, machine work, and another set of pistons...but it runs great, and I don't want to have to break it back down if its not necessary. Have any of you guys used permatex to seal the cases before? If nay, how about some recommendations of gasket suppliers. If I go back into it, I'll only use OEM crank seals, and of course threebond. Also, what about porting the 760 cylinders. Any recommendations on where to send them to? What kind of performance gains can I see if I have them ported/windowed out? Thanks for all the advice I get!


  2. #2
    Myself's Avatar
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    I've used so many aftermarket crank seals I can't even count them. Never had any problems. Only thing I'd worry about is if the Permatex you used is resistant to fuel and alcohol. Search for specs or an MSDS sheet for it. If so then you're OK. If not, then I'd be worried about breakdown from the fuel and a possible air leak at the case mating surface. You can get nice overall gains from Yamaha cylinders just by matching up the sleeves to the actual ports. They are terrible from the factory.

  3. #3
    Did you pressure test the block befor you dropped it back in ???? Like the old saying goes "If it aint broke dont fix it"...........but I would take the compression guage with me and check the cylinders every few hours or so..

  4. #4
    Fortunately pressure testing these motors is pretty easy provided that you remove the exhaust and carbs. Its also just as easy to pressure test the water jacket separately from the engine (Remove only exhaust for that)

    I'd also suggest running 93 octane and premix. Ditch the stock oil injection system.

  5. #5

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    Quote Originally Posted by butterbean_29512 View Post
    Also, what about porting the 760 cylinders. Any recommendations on where to send them to? What kind of performance gains can I see if I have them ported/windowed out? Thanks for all the advice I get!
    Send your head and cylinder to Harry and Gerhardt Klemm at www.groupk.com . They will give you a mild port and more than likely reshape your domes on the head, along with jetting recomendations for your stock carbs. The boat will run quicker with a tad more top end.

    Give them a call and talk to them about your head.... tell them exactly what you have already done to it. They will probably question you about your method for checking compression. You probably will also have to get a little taller impeller..... which you should be able to get used on this forum in the "for sale" section. Their mods are conservative, designed to get the most out of the boat and still maintain reliablity.

  6. #6
    elmatta's Avatar
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    I rebuilt the engine using permatex #2 (turboseal) to seal the cases, not threebond, used the cheapo crank seals off ebay (I was on a budget back then), and no pressure test of the engine.
    3 very important things you neglected on man. Even on a budget, the sealant and the crank seals are not that expensive and the pressure tester is always a good thing to have. I would keep an eye out on the comp of the cylinders before and after you ride which is basic maintenance anyway. Other then that, keep on riding it as it is right now because:

    before actually learning anything about the two strokes
    You should ride, enjoy and learn about a ski before you mod it. (Unless of course they are basic safety mods or bolt on go-fast parts)

  7. #7

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    just an update on what I decided to do....I did take it apart to check it. Fuel/oil residue was in the flywheel area, so I know it was at least leaking there. It also showed signs of running a little lean, had very little piston wash on the top of the pistons. Cylinders look to have been ported already. Although it did run well, it loaded up in no wake zones. Cylinders and cases are at the machine shop, cylinders will get a light hone to remove any glaze, and the cases will be trued on the sealing flanges. Crank bearings look good, make a light sound when you spin them, but are perfectly smooth with no rough spots. Seems like I dodged a bullet with it.

  8. #8
    Sounds like you are spending a bunch of money on machine work. This time, put it all together and then pressure test the crankcase before putting the carbs and complete exhaust on it. Aftermarket or not, seals sometimes don't "seal" and things like the base gasket and other points can leak also. Follow OsideBill's tutorial on rebuilding and you should be golden. Here's the link for installing the crank. Also another thread for the pressure testing .

    http://www.greenhulk.net/forums/showthread.php?t=144536
    http://www.greenhulk.net/forums/showthread.php?t=9408

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